This invention relates generally to improved unitized in-line and delta-configured guns for color cathode ray tubes, and is specifically addressed to an improved electrode structure for such guns that enhances picture resolution.
Unitized electron guns generate three electron beams developed by cathodic thermionic emission. The resulting beams are formed and shaped by a tandem succession of electrodes spaced along the central axis of the gun. The electrodes cause the beam to be focused on multiple phosphor groups located on the faceplate of a color cathode ray tube. A prime objective in the design of such guns is to provide small beam spot size with enhanced picture resolution. Unitized guns may be of the in-line type, or may be of triangular or "delta" configuration.
A problem arises in the design and construction of unitized guns in that the beams must travel in close proximity because of the space restriction of the narrow confines of the neck of the cathode ray tube in which the guns lie. If the beam passageways do not provide shielding, the lines of force generated in the electron lens section of the gun, which act to focus the electron beams at the proper point of convergence on the viewing screen, will interact and exert an undesired effect on the beams as they pass between and through the electrodes. Any such "crosstalk" can result in deforming the beams within the electrode structures so that the beams become elliptical at their points of landing. This ellipticity must be compensated for at the penalty of an undesired increase in spot size.
This problem of deleterious interaction of the fields is negligible in those non-unitized guns wherein each beam travels through a separate discrete tunnel formed by a series of individual "barrels" extending from the source of the beam at each cathode through to the convergence assembly at the opposite end of the gun.
A common system of electrode forming is by means of dies which can produce large quantities of identical components that meet tight tolerance requirements. In U.S. Pat. No. 3,873,897 issued to Hughes, examples of economical die-formed electrodes are shown that are deep-drawn in matching cup-like sections which are mated at annular flanges projecting from the cup faces and bonded by spot-welding. This design does not provide internal shielding, however and, the result can be undesired distortion of the beams due to interactive effect.
In U.S. Pat. No. 3,890,528, Say recites a focusing electrode structure for a tri-potential, delta-configured electron gun, or an in-line unitized gun, having offset electrode apertures for convergence wherein improved shielding of the apertures is provided by lips extending a short distance into the focusing electrode aperture for each beam. The stated objective of the Say invention is to effect improved control of the lines of force in the low beam velocity area (i.e., better focusing effects) of each discrete electron beam. The patent does not address itself to the continuous internal shielding of the beams to prevent mutual field interaction in their passage through the electrode.
In Pat. U.S. No. 24 38 234 (German), a scheme is recited wherein the beam-passing apertures in the opposing faces of cup-like electrode sections used in delta-configured or in-line guns are augmented by superimposing one or more unitized plates upon them which come together to define a very short beam-passing tube. However, the objective is to extend the axial lip structure so as to improve the symmetry of the electrical field between opposing openings. The patent does not show the use of inserts to permit the construction of an elongated electrode with a beam-passing tube all the way through.